Adjust Bounce Rate in Google Analytics.

Use timer and GA event so that visitors who visit only one page, but
stay on it for >= 30 seconds, are _not_ counted as a "bounce".
Experiment with watch doing a quick build of one .md file.
Merge branch 'master' of github.com:greghendershott/frog

* 'master' of github.com:greghendershott/frog:
  Mention tested on Ubuntu.
  Deterministic footnote anchors.
  On Unix set `external-browser` to sensible-browser.
  Mention how to install `easy_install`.